1. Technical Field
This invention relates, generally, to load lifting method and apparatus, and specifically, to methods and apparatus for lifting heavy loads, for example, air conditioner compressors from ground level, or near ground level, to levels above the ground, for example, to flat roofs one or two floors above the ground.
2. Background of the Invention
The prior art is replete with attempts to lift heavy objects, for example, air conditioning compressors, from the ground, or from the back of the pickup truck, to a flat roof such as the roof of a one-story commercial building, or to the attic floor of a residential house being constructed.
Most of the prior art attempts to solve the problem involve the use of a ladder, which in the commencement mode, is set up on the ground, several feet from the structure upon which the load is to be lifted, and in a vertical, or near vertical position.
Typical of this prior art approach is the system illustrated and described in U.S. Pat. No. 4,770,273 to W. H. McMakin, et. al. In both of the embodiments illustrated in FIGS. 1 and 2 of that patent, after the load is lifted vertically above the roof level, the load is moved horizontally by either the human operator of FIG. 1 moving backward away from the ladder, or the tripod of FIG. 2 is moved backward to pivot the ladder away from vertical, towards the structure, to thus place the load above the roof. This process is dangerous in that the swinging load and the pivoting ladder can fall and cause damage to property and to the personnel working below.
U.S. Pat. No. 4,911,266 to W. H. McMakin, et al, is a continuation-in-part of U.S. Pat. No. 4,770,273 and also describes the pivoting of the ladder to swing the load over above the roof.
Additional prior art patents include U.S. Pat. No. 4,183,423 to James P. Lewis; U.S. Pat. No. 4,598,795 to Kevin Larson; U.S. Pat. No. 4,690,248 to Walter H. Killeen; U.S. Pat. No. 5,139,108 to Ivan G. Pate; U.S. Pat. No. 5,265,742 to Donald D. Stenger, et al; U.S. Pat. No. 5,738,185 to M. R. Sears; and U.S. Pat. No. 6,244,381 B1 to Timothy E. Ruble.
While each of these prior art patents shows ways for providing a vertical lift to a load, none of them shows a way to move the load horizontally without swinging the load.
It is therefore the primary object of the present invention to provide new and improved methods and apparatus for lifting heavy objects between vertically spaced locations without swinging the objects.
It is also an object of the invention to provide new and improved methods and apparatus for lifting heavy objects between vertically spaced and horizontally spaced locations.